Composite casting



June 17, 1930. j HOY 1,764,725

COMPOS ITE CASTING Filed March 29, 1924 INVEN TOR.

ATTORN 5 Patented June 17, 1930 UNITED STATES PATENT OFFICE JOHN E. HOY,. OI MIDLAND, MICHIGAN, ASSIGNOR TO THE DOW CHEMICAL COMPANY,

OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN COMPOSITE CASTING Application filed March 29, 1924. Serial No. 702,996

In order to overcome the undue expansion of internal combustlon englne pistons formed i of lightmetal alloys, as well as for the sake of the better bearing contact that is obtained between the cast iron cylinder bore and a piston having a skirt 1i ewise of cast iron or of steel, a variety of pistons have been proposed having a composite structure. That is, the bodies of such pistons have been made of a light metal alloy, for example, one of the numerous magnesium base alloys available for the purpose, and-the skirt of the piston has beenisurrounded by, or encased in, a shell of cast iron or steel, or one or more iron bands, as distinguished from the loosely fitting piston ring, have been attached to the piston skirt. A serious difliculty, however, is encountered whenever it is thus attempted to firmly attach to alight metal piston, with its relatively high coefiicient of expansion, a band of metal having a lower coefiicient of expansion. In other words, when such a composite piston is subjected to the changes of temperature encountered in the operation of an internal combustion motor the band will either work loose or the piston skirtbe so distorted as to detractseriously from the utility of the device.

The object of the present invention is the production of alight metal alloy piston, primarily one designed for use in internal combustion engines, to which piston is permanently attached one orv more bands of cast iron or steel in such a manner as alwa s to remain firmlyin contact with the piston body proper, irrespective of changes in tempera-' forms one of the composite parts of such piston, such shell being shown separate from the piston.

In its general features of construction, my present improved piston is similar to those of cast iron or light metal alloys heretofore used in internal combustion engines. In other words, such piston comprises a more or less cylindrical head portion 1, from which depends a sleeve or skirt portion 2. The latter is formed with oppositely placed inwardly directed bosses 3, which are apertured to receive the wrist pin (not shown), whereby the piston is attached to the connecting rod. Bushings 4 of bronze or equivalent bearing metal are preferably fitted to the apertures in such bosses and an integral rib 5 between each boss and the head 1 contributes to the strength of the structure. In order effectually to seal the piston within the walls of the cylinder in which it works, resilient piston rings (not shown), of familiar construction, are seated in annular recesses 6 in the head portion 1, as'need not be here explained.

The present improvement in the specific form illustrated consists in the application to the skirt portion 2 of a shell or band 7 that entirely surrounds the same adjacent its lower edge, such shell being formed on opposite sides with vertically extending portions 8 that rise approximately to the height of the wrist pin axis but are located half way between the respective ends of such wrist pin, or in other words between the openings in bosses 3. The exterior surface ofsuch shell 7, including the portions 8 thereof just referred to, is strictly cylindrical to'conform with the cylindrical surface of the piston skirt 2 and of the same diameter as the latter. It will be understood, in other words, that the metal composing the piston proper (head 1 and skirt 2) is cast in a suitable mold in which such shell has been previously placed, the walls of the mold being formed 5 to give the proper contour to the exposed portions of the body and skirt. The exterior surface of the latter, including the lower edge 9 thereof, which projects below the lower edge of the shell, will accordingly lie flush 10 with the exterior surface of the shell.

As best shown in Figs. 3 and 4, the shell is provided with a plurality .of inwardly projecting studs 10. These are of general conical form, their free or inner ends being larger than their outer ends which merge in the material of the shell and they are referably formed inte ral with the latter. uch shell, as shown in tile same figures, is further provided with a plurality of openings 11 which are likewise of general conical form,

5 as to extend through the metal of the skirt into and fill the openings 11 in the shell, so

when the latter is cast within the shell, so that the heads of such studs lie substantially flush with the inner surface of the skirt. The metal of the latter in casting will also flow that the skirt is in effect provided with a complementary series, of studs 12 (see Figs. 2 and 4) that have their larger ends directed outwardlyand lying substantially flush with the outer surface of the shell.

The several studs 10 and 12, wherewith the piston skirt and the shell that surrounds the 'same are thus provided, will preferably be spaced in staggered relation circumferentially about the parts in question and also vertically where, as in the preferred construction shown,.the shell comprises the two opposite upstandin portions 8.

' The stu s or lugs 10 on the shell not only serve to center the latter around the core in the operation of casting the piston, but also clench the skirt to such shell when the piston is poured. A similar clenching effect is likewise obtained by the reversely directed studs or lugs 12 that are formed by the metal of the skirt which fills the countersunk openings 11 in the shell. As a result of the foregoing con struction, any tendency on the part 'of the shell to become loose on the piston skirt, incidentally to changes of temperature, due to the; different-coefficients of expansionof the metals composing the parts in question, is counteracted inasmuch as the flaring studs 10 on the shell and the oppositely flaring studs 12 onthe skirt will seat more tightly, whether the skirt contracts more rapidly than the shell or theshell expands more rapidly than the skirt. The effect, of course, of expansion of the skirt at a rate in excess of that of the shell I forcibly against the latter. Furthermore, the

projections of the metal of the skirt in the form of studs 12 through openings 11 in the shell affords a direct path for the conduction of heat from the body of the piston to the cylinder wall, to this extent obviating the objection to composite pistons of the type in hand, viz., that the escape of heat from the piston is interfered with because of the lower thermalconductivity of the shell.

It will be understood, of course, that the body of the piston may be either cast or forged and that the particular manner of fabrication of the surrounding shell, whether, in other words, it be a casting, stamping, or forging, does not affect the principle involved in my invention. .It has already been explained that the shell neednot be of the particular form shown by way of illustration in the drawing, but that it may consist of a simple band without, in other words, the upstandin portions 8; also that a plurality of vertical y spaced bands, instead of a single band or shell, may be utilized if found desirable. While I have hereinbefore spoken of the light metal alloy, whereof the piston body proper is composed, as being a magnesium base alloy, i. e. one in which magnesium is the predominant constituent, it will be understood that pistons made of any equivalent alloy, such as the well known aluminum base alloys, may be advantageously fitted with a shell of another metal or alloy in the manner hereinbefore described and better bearing qualities thus secured 'for such piston while at the same time avoiding the difiiculties that have hertofore inhered in pistons of composite construction.

Other modes of applying the principle of my invention may be employed instead of the one explained, change'being made as regards the mechanism herein disclosed, provided the means stated by any of the following claims or the equivalent of such stated means be employed.

I therefore particularly point out and disstinctly claimas my invention g 1. In a piston, or like article, the combination with a head and integral skirt depending therefrom; of a cylindrical shell closely surrounding said skirt and composed of a material having a different so-efiicient of expansion, said skirt and surrounding shell each having a plurality of projections extending through to the respective surfaces and formed to have clinching engagement and an even surface level.

2. In a piston or like article, the combination with a head and integral skirt depending therefrom of a cylindrical shell closely surrounding said skirt and composed of a material'having a different co-eflicient of expansion, said skirt and surrounding shell each having a plura ity of projections" ex-- merely presses the former that much more tending through to the respective surfaces and being of general conical form with their free ends the larger whereby said head and shell are clinched together.

3. In a piston, the combination with a body comprising a head and an integral skirt depending therefrom, said body being composed of a light metal alloy and a cylindrical shell of ferrous metal surrounding said skirt, the latter and said shell each having a plurality of projections extending through to the respective surfaces and formed to have clinching engagement and an even surface level;

4. In a piston, the combination with a body comprising a head and an integral skirt depending therefrom, said body being composed of a light'metal alloy; and a cylindrical shell of ferrous metal surrounding said skirt, the latter and said shell each having a plurality of projections extending throng to therespective surfaces and being of a general conical form with their free'ends the arger whereby: said body and part are clenched together.

5. In a piston, the combination with a body comprising a head and an integral skirt depending therefrom, said body being composed of a light metal alloy; anda cylindrical shell of ferrous metal surrounding said skirt, said shell being formed with holes wherein the material of said skirt extends, v

and such holes and the corresponding lugs on said skirt being of general conical form with walls converging to points within the piston.

Si ned by me this 26th day of March,

JOHN E. HOY. 

